ESP32 one-click download circuit notes

Burning conditions:

When EN rises,
IO0 remains low
---------> Entering the download startup mode

IO2 does not affect entering the download, but in order to prevent users from multiplexing this pin, it should be kept on IO2 when programming. The control pulls low

Circuit Design Analysis:

The structure is similar to the RS flip-flop.
By controlling the triode, this signal can only be pulled down
/--------------------------------- -------------------------------/
When the RTS and DTR levels are the same, the triodes are all cut off, and at this time IO1 and EN The level state is determined by the pull-up circuit
. When the RTS and DTR levels are different, RTS=EN, DTR=IO0.
To make the circuit enter the programming mode, we need to make
IO=0, EN=0
------>
IO=0, EN=0–>1 (rising edge)
truth table

DTR = 0; RTS = 0, 此时Q1截止，Q2截止，EN = 1; IO0 = 1  //EN外部上拉，此电路图中没有表示出来
DTR = 0; RTS = 1，此时Q1截止，Q2导通, EN = 1; IO0 = 0
DTR = 1; RTS = 0, 此时Q1导通，Q2截止, EN = 0; IO0 = 1
DTR = 1; RTS = 1, 此时Q1截止，Q2截止, EN = 1; IO0 = 1

in conclusion

Therefore, it is concluded that when downloading, you only need to use the CH340x debugger to connect to 5 wires, which are VCC, GND, TX, RX, and RTS, and then the firmware can be burned normally.

Reference:
Principle Analysis of ESP8266/ESP32 Automatic Download Circuit
ESP32 Automatic Download Circuit